Imaging system

ABSTRACT

A method of selectively producing positive or negative photoelectrophoretic copies is described. A suspension of photosensitive particles sensitive to a first range of wavelengths is placed between two electrodes, one of which is transparent and the other of which has a surface sensitive to a second range of wavelengths. When a field is imposed across the suspension and an image is projected through the transparent electrode using radiation in only one of said first and second ranges, a positive or negative image is formed on a given electrode, depending on whether the electrode or the suspension is sensitive to the radiation used.

United States Patent [4 1 June 13, 1972 Tulagin [54] IMAGING SYSTEM [72]Inventor: Vsevolod Tulagin, Rochester, NY.

[73] Assignee: Xerox Corporation, Rochester, NY.

[22] Filed: Jan. 29, 1970 [2!] Appl. No.: 12,532

Related US. Application Data [62] Division of Ser. No. 675,892, Oct. 17,1967 [52] US. Cl ..204/299, 204/300, 204/ 1 81 [51] Int. Cl. ..BOlk5/02, C23b 13/00 [58] Field of Search ..204/181, 299, 300; 96/1; 355/3[56] References Cited Primary Examiner-John H. Mack AssistantExaminer-A. C. Prescott Att0rneyRonald Zibelli and James A. Ralabate 57] ABSTRACT A method of selectively producing positive or negativephotoelectrophoretic copies is described. A suspension of photosensitiveparticles sensitive to a first range of wavelengths is placed betweentwo electrodes, one of which is transparent and the other of which has asurface sensitive to a second range of wavelengths. When a field isimposed across the suspension and an image is projected through thetransparent electrode using radiation in only one of said first andsecond ranges, a positive or negative image is formed on a givenelectrode, depending on whether the electrode or the suspension issensitive to the radiation used.

3 Claims, 1 Drawing Figure PKTENTEDJUM 13 I872 INVENTOR. VSEVOLODTULAGIN MM ATTORNEY IMAGING SYSTEM This is a division of U.S.application Ser. No. 675,892, filed Oct. 17, 1967.

BACKGROUND OF THE INVENTION This invention relates to imaging systemsand, more specifically, to improved electrophoretic imaging systems.

There has been recently developed an electrophoretic imaging systemcapable of producing monochromatic or polychromatic images whichutilizes electrically photosensitive particles. This process isdescribed in detail and claimed in copending applications Ser. Nos.384,737 now U.S. Pat. No. 3,384,565, 384,681 abandoned in favor ofcontinuation-inpart Ser. No. 655,023 now U.S. Pat. No. 3,384,566 and384,680 abandoned in favor of continuation-impart Ser. No. 518,041 nowU.S. Pat. No. 3,383,993 all filed July 23, 1964. In this imaging system,colored light absorbing particles are suspended in a non-conductiveliquid carrier. The suspension is placed between electrodes, subjectedto a potential difference and exposed to an image. As these steps arecompleted, selective particle migration takes place in imageconfiguration, providing a visible image at one or both of theelectrodes. An essential component of this system is the suspendedparticles which must be electrically photosensitive and which apparentlyundergo a net change in charge polarity upon exposure to activatingelectromagnetic radiation, through interaction with one of theelectrodes. In a monochromatic system, particles of a single color areused, producing a colored image equivalent to a conventionalblack-and-white photograph. in a polychromatic system, the images areproduced in natural color because mixtures of particles of two or moredifferent colors which are each sensitive to light of a specificwavelength or narrow range of wavelength are used.

Ordinarily, as further described below, the suspension is exposed to theimage through a conductive transparent electrode called the injectingelectrode. The other electrode called the blocking electrode has asubstantially insulating surface and may be opaque. Ordinarily, apositive image is formed on the transparent injecting electrode while anegative image is often formed on the blocking electrode. Where it isdesired that the positive copy be used on an opaque background, theimage must be transferred from the transparent injecting electrode to areceiving sheet such as paper. Since this transfer step adds complexityto the system, it would be desirable to be able to form a positive imageon the blocking electrode which could be the final image-supportingsheet. Also, there are problems where original input may be eitherpositive and negative since the image formed on a given electrode wouldalways be the same or the reverse of the original input. It would, thus,be desirable if a positive or a negative image could be selectivelyobtained on a given electrode. Thus, there is a continuing need,especially in monochromatic imaging, to form selective positive ornegative images in a convenient and simple manner.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide an electrophoretic imaging system overcoming the above-noteddisadvantages.

Another object of this invention is to provide a method of selectivelyproducing positive or negative electrophoretic images.

Still another object of this invention is to provide an electrophoreticimaging system capable of producing positive images from both negativeand positive input.

The above objects and others are accomplished in accordance with thisinvention by incorporating in the blocking electrode in anelectrophoretic imaging system a photosensitive ingredient of limitedphotosensitive response selected so as to cause some particles to bereflected from the blocking electrode to the injecting electrode to agreater degree than other particles.

The pigment reflection phenomenon of this invention may be also used inmonochromatic electrophoretic imaging to permit an operator toselectively produce positive or negative copies of an original. In thisembodiment, a photosensitive ingredient having a narrow spectralresponse, e.g., to red light only, is incorporated into the blockingelectrode. The imaging suspension is made up of single color particleshaving a different narrow spectral response, e.g., to blue light.Exposing this suspension to an image by means of blue or cyan lightproduces a positive image on the injecting electrode and a positiveimage on the blocking electrode while exposing to red or white lightproduces a negative image on the injecting electrode and a positiveimage on the blocking electrode. Thus, positive or negative images canbe made on the desired electrode from a specific original by merelyfiltering the exposure light. In this description, the particular colorsmentioned are merely exemplary. In general, exposing by means of a lightcolor to which the suspension responds will give a negative image whileexposing by means of light having a color to which the blockingelectrode photosensitive ingredient responds will produce a positiveimage on the blocking electrode. Thus, many combinations of blockingelectrodes, photosensitive ingredient and imaging particles arepossible.

BRIEF DESCRIPTION OF THE DRAWING The invention may be further understoodupon reference to the drawing which shows a schematic representation ofapparatus for performing the improved electrophoretic imaging process ofthis invention.

Referring now to the HQ, there is seen a transparent electrode generallydesignated 1 which in this exemplary instance is made up of a layer ofoptically transparent glass 2 overcoated with a thin opticallytransparent layer 3 of tin oxide, commercially available under the nameNESA glass. This electrode will hereafter be referred to as theinjecting electrode. Coated on the surface of injecting electrode 1 is athin layer 4 of finely divided photosensitive particles dispersed in aninsulating carrier liquid. The term photosensitive for the purposes ofthis application refers to the properties of a particle which, onceattracted to the injecting electrode, will migrate away from it underthe influence of an applied electric field when it is exposed to actinicelectromagnetic radiation. For a detailed theoretical explanation of theapparent mechanism of operation of the particle migration, see the abovementioned copending applications Ser. Nos. 384,737, 384,681 and 384,680,the disclosures of which are incorporated herein by reference. For thepurposes of this invention, the photosensitive particles should have arange of wavelengths of electromagentic radiation to which they aresensitive and a second range to which they are non-sensitive. The extentof these ranges is not significant. As is further pointed out below, agreat many compositions have this characteristic of sensitivity to somewavelengths and insensitivity to others.

Particle suspension 4 may also contain a sensitizer and/or a binder forthe pigment particles which is at least partially soluble in thesuspending liquid. Adjacent to the liquid suspension 4 is a secondelectrode 5, hereinafter called the blocking electrode" which isconnected to one side of the potential source 6 through a switch 7. Theopposite side of potential source 6 is grounded as is the conductivesurface of injecting electrode 1 so that when switch 7 is closed, anelectric field is applied across the liquid suspension 4 betweenelectrodes 1 and 5. in this embodiment, electrode 5 is made in the formof a roller having a conductive central core 8 connected to thepotential source 6. The core is covered with a layer of a blockingelectrode material 9, which may be insulating or substantiallyinsulating. In the system of this invention, the layer 9 will include aphotosensitive ingredient which is insulating except when exposed toactinic electromagnetic radiation. The photosensitive ingredient inlayer 9 should be sensitive only to a narrow range of wavelengths andsubstantially insensitive to another range of wavelengths. Theingredient in layer 9 should be selected with respect to the particlesin suspension 4 so that particles 4 should be sensitive to radiation towhich layer 9 is insensitive while layer 9 should be sensitive to otherradiation to which layer 4 is insensitive. Thus, by suitable filtrationof a radiation source, the system may be exposed to radiation to Y whicheither layer 9 or particles in suspension 4 would selectively respond.

An image projector made up of a light source 10, a transparency 11 and alens 12 is provided to expose the dispersion 4 to a light image of theoriginal transparency 11 to be reproduced. Filters 13 and 14 may beselectively interposed between light source 10 and transparency 11 tocontrol the wavelength of the radiation directed against suspension 4.

The particle suspension is exposed to the image to be reproduced withthe desired radiation while a potential is applied across the blockingand injecting electrodes by closing switch 7. Roller 5 is caused to rollacross the top surface of injecting electrode 1 with switch 7 closedduring the period of image exposure. Where the filter 13 or 14 isselected so that the electromagnetic radiation falling on the suspensionis in the range to which the particles are sensitive but layer 9 isinsensitive then a positive image corresponding to transparency 11 isformed on injecting electrode 1 with a negative image forming onblocking electrode 5. On the other hand, if the filter 13 or 14 isselected so that the radiation falling on the suspension is in the rangeto which layer 9 is sensitive but particles and suspension 4 isinsensitive then a negative image is formed on the injecting electrode 1with a positive image on blocking electrode 5.

While the mechanism of this image reversal is not fully understood, itis thought that where the radiation is such as to activate the imagingparticles the exposed particles have charge injected thereinto andmigrate to a blocking electrode 5 leaving the unexposed particles oninjecting electrode 1 thus producing a positive image. Where theradiation is such that layer 9 is sensitive then charge is injectableinto the particles from layer 9 in exposed areas (since in exposed areasphotosensitive 9 becomes conductive). Thus, particles in exposed areasare reflected from layer 9 to the injecting electrode surface. Thisproduces a negative image on injecting electrode 1.

After the image is formed the desired image may be cleaned from theelectrode and the desired image may be preserved. Where the desiredimage is on blocking electrode 5, it may be fixed to layer 9 with layer9 replaced with a new sheet of blocking electrode material forsubsequent imaging operations. Where the desired image is formed oninjecting electrode 1, it is desirable to transfer the particulate imageto a receiving sheet to make the system ready for subsequent imagingoperations. In such a case a second roller generally indicated at 15 maybe provided. This transfer roller 15 comprises a conductive central core16 having on its surface an insulating or substantially insulatingreceiving sheet 17. Conductive core 16 is connected through power supply18 and switch 19 to ground. Thus, when switch 19 is closed and roller 15is passed across the injecting electrode 1 surface after an image hasbeen formed using blocking electrode 5, a field is imposed across theparticulate image between roller 15 and injecting electrode 1. It shouldbe noted that the sign of the potential imposed on the conductive coreof roller 15 is opposite to that of the potential imposed on the core ofblocking electrode 5. As transfer roller 15 passes across injectingelectrode 1, the formed image transfers to the surface of receivingsheet 17. Transfer efficiency may be increased if the original image isprojected onto the injecting electrode surface or said surface isflooded with white light. The image may then be fixed to the surface ofreceiving sheet 17 and receiving sheet 17 may be replaced with a cleansheet for further imaging operations.

The roller configuration shown for blocking electrode 5 and transferroller 15 are merely exemplary. For example, each of these members maybe in the form of an endless belt entrained around rollers or mayinclude a web of blocking electrode material 9 or receiving sheetmaterial 17, respectively, fed

from a feed roll around the conductive cores to take up roll. Also, ifthe desired image is formed on blocking electrode 5 and it is notdesired to preserve the image formed on injecting electrode 1, a brushor wiper blade, may be provided to clean the surface of injectingelectrode 1 between imaging cycles.

Any suitable electrically photosensitive material having the desiredspectral response characteristics may be used in the particulatesuspension or in the blocking electrode surface layer. Mostphotosensitive materials have the desired electrical spectral responsecharacteristics. For example, cyan colored particles are generallyprimarily responsive to red light, yellow colored particles aregenerally primarily responsive to blue light and magenta coloredparticles are generally primarily responsive to green light.

For many uses, it would be preferred to use a black or darkly coloredphotosensitive material which had a range of radiation wavelengths towhich it did not respond. On the other hand, for some uses awhite-appearing material might be preferred. Many white-appearingphotosensitive materials have their primary response in the ultravioletregion. These particles could be used with a special efiectiveness inconjunction with a colored photosensitive material responsive to visiblelight but substantially non-responsive to ultraviolet light. Anexcellent combination might consist of a white-appearing ultravioletsensitive material on the surface of the blocking electrode withblack-appearing photosensitive particles in the suspension which aresubstantially transparent to ultraviolet light. This would simplify theproduction of black-on-white copies. Typical materials which havephotosensitive response substantially limited to ranges of wavelengthsof electromagnetic radiation include: Algol Yellow GC, l,2,5,6-di(C,C'-diphenyl)-thiazole-anthraquinone (General Dyestuffs); GraphtholRhodamine, the molybdenum lake of 3,6-bis (diethylamino)-9,2-carbethoxyphenyl xanthenonium chloride (Sandoz lnc.); Bonadur Red B,l-(4-ethyl-5'- chloroazobenzene-2 -sulfonic acid )-2-hydroxy-3-naphthoicacid calcium lake (American Cyanamide); lndanthrene Brilliant Orange RK,4,l0-dibromo-6,lZ-anthanthrone (General Dyestuffs); Calcium Lithol Red,a calcium lake of l-(2- azonaphthalene-l'-sulfonic acid)-2-naphthol(Collway Colors); Indofast Violet Lake, a dichloro-9,l8- isovioianthrone(Harmon Colors); Cyan Blue GTNF, the beta form of copper phthalocyanine(Collway Colors); lndofast Yellow Toner, flavanthrone (Harmon Colors);Cyan Green 15-3100, a chlorinated copper phthalocyanine (AmericanCyanamide); Methyl Violet, a phosphotungstomolybdic lake of 4-(N,N,N-trimethyl anilino )-methylene-N", N"- dimethylanilinium chloride(Collway Colors); Diane Blue, 3 ,3 '-methoxy-4,4'-diphenyl-bis( 1'-azo-2' -hydroxy-3 naphthanilide) (Harmon Colors); Monolite Fast BlueGS, a mixture of alpha and beta metal-free phthalocyanine (ArnoldHoffman Company); Duol Carmine, a calcium lake of l-(4-methylazobenzene)-2-sulfonic acid)-2-hydroxy-3-naphthoic acid (E. l. duPont de Nemours & Co.); Naphthol Red B, l-(2 -methoxy-5 '-nitrophenylazo2-hydroxy-3 '-nitro-3- naphthanilide (Collway Colors); Quindo MagentaRV-6803, a substituted quinacridone (Harmon Colors); Vulcan Fast RedBBE, 3,3'-dimethoxy-4,4'-biphenyl-bis (l'-phenyl-3-methyl-4"-azo-2"-pyrazolin-5"-one) (Collway Colors); Watchung Red B,l-(4-methyl-5'-chloroazobenzene-2-sulfonic acid)-2-hydroxy-3-naphthoicacid (E. l. du Pont de Nemours & Co.); and mixtures thereof. Othertypical electrically photosensitive pigments include the followingdescribed in the noted copending applications:8,13-dioxodinaphthol,2-2,3' )-furan-6-carbox-4 '-methoxyanilide (Ser.No. 421,377 now U.S. Pat. No. 3,448,029, filed Dec. 28, 1964); 1-cyano-2,3-( 3 '-nitro)-phthaloyl-7,8-benzopyrrocoline (Ser. No. 445,235now U.S. Pat. No. 3,402,177, filed Apr. 2, 1965); N-2 'pyridyl-8, l3-dioxodinaphtho-( l,2-2,3 )-furan-6-carboxamide (Ser. No. 421,281 nowU.S. Pat. No. 3,447,922, filed Dec. 28, 1964); various quinacridones asdisclosed in application Ser. No. 468,935, filed July 1, 1965;anthraquinones as disclosed in application Ser. No. 467,344 nowabandoned,

filed June 28, 1966; azo pigments as disclosed in application Ser. No.473,607 abandoned in favor of continuation-impart Ser. No. 737,689 filedJune 17, 1968, filed July 21, 1965; dioxazine pigments as disclosed inapplication Ser. No. 519,104 now U.S. Pat. No. 3,442,781, filed Jan. 6,1966; phthalocyanines as disclosed in application Ser. No. 560,603,filed June 27, 1966.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples furtherspecifically define the present invention with respect to the selectiveformation of positive and negative photoelectrophoretic images. Partsand percentages are by weight unless otherwise indicated. The examplesare intended to illustrate the various preferred embodiments of theprocess of the present invention.

All of the following examples are carried out in apparatus of thegeneral type illustrated in the FIGURE with the imaging mix 4 coated ona NESA glass substrate through which exposure is made. The NESA glasssurface is connected in series with a switch, a potential source and aconductive center of a blocking electrode having a sensitized layer onits surface. After images are formed, the NESA glass surface isconnected in series with a switch, a second potential source and theconductive center of the transfer roller. A negative potential of about3,000 volts is imposed on the core of the blocking electrode rollerwhile a positive potential of about 3,000 volts is imposed on the coreof the transfer roller. Each roller is approximately 2 /2 inches indiameter and is moved across the plate surface at about 4 centimetersper second. The plate employed is roughly 3 inches square and is exposedwith an unfiltered white light intensity of about 8,000 foot-candles asmeasured on the uncoated NESA glass surface. Unless otherwise indicated,about 7 percent by weight of the indicated pigment in each example issuspended in Sohio Odorless Solvent 3,440, a kerosene fraction availablefrom the Standard Oil Company of Ohio. Exposure is made with a 3,200 K.lamp through a conventional black-and-white transparency and the filteris mentioned in the specific examples.

EXAMPLE I The surface of the blocking electrode is sensitized bydispersing a finely divided photosensitive cyan-colored pigment,Moholite Fast Blue GS, the alpha form of metal-free phthalocyanine, C.I. No. 74,100, available from the Arnold Hoffman Company, in SohioOdorless Solvent 3,440. A cotton wad is dipped in this dispersion andrubbed on the surface of a sheet of Baryta paper. The Sohio OdorlessSolvent 3,440 is allowed to evaporate leaving a blue-green coloredsurface on the Baryta paper. The phthalocyanine particles do not form auniform coating but are dispersed on and embedded in the paper surface.The sensitized paper is then wrapped around a roller electrode as shownin FIG. 1. A particle suspension is prepared consisting of about sevenparts of a photosensitive magenta pigment, Watchung Red B, a barium saltof l-(4'- methyl-5-chloroazobenzene-2-sulfonic acid)-2-hydroxy-3-naphthoic acid, C. I. No. 15,865, available from E. I. du Pont deNemours & Co., in about 100 parts Sohio Odorless Solvent 3,440. Thesurface of the NESA glass is coated with this suspension. A Wratten 29filter (which transmits only red light) is placed between the lightsource and the transparency to be copied. A potential is imposed betweenthe blocking electrode core and the injecting electrode and the blockingelectrode is passed across the imaging suspension. Since the suspendedmagenta pigment particles do not absorb the red light while thephthalocyanine-sensitized blocking electrode surface does absorb redlight, a negative image is formed on the NESA electrode and a positiveimage on the blocking electrode surface. The transfer roller is thenpassed across the injecting electrode while a positive potential isimposed on the transfer roller core. The particulate image transfers tothe surface of the transfer roller where it may be fixed by laminating aclear film thereover.

The surface of the blocking electrode is cleaned and a fresh transfersheet is wrapped around the transfer roller. The surface of theinjecting electrode is again coated with a dispersion of Watchung Red Bparticles in Sohio Odorless Solvent 3,440. Instead of the Wratten 29filter, a Wratten 61 filter is placed between the light source and thetransparency to be copied. This permits only green light to fall on theinjecting electrode. The blocking electrode is again passed across theinjecting electrode surface. Here, the blue-green blocking electrodesurface does not absorb the green light while the red-magenta particlesdo absorb the green light. Thus, a positive image is formed on the NESAelectrode with a negative image on the blocking electrode surface. Theimage formed on the injecting electrode surface is then transferred bypassing the transfer electrode again across the injecting electrode.

Good quality positive and negative images are thus produced on areceiving sheet merely by shifting filters into and out of the lightpath of the projection system.

Example II Particles of a finely divided yellow pigment, N-2"-pyridly- 8,1 3-dioxodinaptho-( 1,2-2 ',3 )-furan-6-carboxamide, prepared by theprocess described in copending application Ser. No. 421,281, filed Dec.28, 1964 is applied to the surface of a Baryta sheet as described inExample 1 above. An imaging suspension is prepared by dispersingfinely-divided particles of Monolite Fast Blue GS in Sohio OdorlessSolvent 3,440. Two imaging cycles as described above are then performed.The first is produced with a Wratten 29 filter in the projection system.This filter permits only red light to pass, which is absorbed by thecyan-colored particle but is not absorbed by the yellow particles on theblocking electrode surface. Thus, a positive image is produced on theinjecting electrode surface. In the second imaging cycle, a Wratten 47bfilter is used. This filter permits only blue light to pass. The yellowparticles on the blocking electrode surface will absorb the blue lightbut the cyan-colored imaging particles will not absorb the blue light.Thus, a negative image is produced on the injecting electrode surface.Each image is transferred to a receiving sheet and fixed thereon.

Although specific components and proportions have been described in theabove examples relating to the selective formation of positive andnegative electrophoretic images, other suitable materials, as listedabove, may be used with similar results. In addition, other materialsmay be added to the electrodes, particles or particle-carrier suspensionto synergize, enhance of otherwise modify their properties. For example,the particles in the suspension or the photosensitive blocking electrodesurface may be dye-sensitized or electrically sensitized, if desired.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

l. Photoelectrophoretic imaging apparatus comprising a firstsubstantially transparent electrode and a second electrode containing anelectrically photosensitive layer said first and second electrodessupported to virtually contact one another and having means for couplingto a voltage source to establish an electrical field between saidelectrodes, and

exposure means for projecting activating electromagnetic radiationthrough said first electrode toward said second electrode.

2. The apparatus of claim 1 and further including light filtering meansfor limiting the wavelength range of the activating electromagneticradiation.

3. The apparatus of claim 1 wherein said electrically photosensitivelayer is sensitive to radiation of wavelengths other than thewavelengths to which an imaging suspension adjacent said electricallyphotosensitive layer is sensitive.

2. The apparatus of claim 1 and further including light filtering meansfor limiting the wavelength range of the activating electromagneticradiation.
 3. The apparatus of claim 1 wherein said electricallyphotosensitive layer is sensitive to radiation of wavelengths other thanthe wavelengths to which an imaging suspension adjacent saidelectrically photosensitive layer is sensitive.